Study On Clad Technology Of Steel Ingot By Implanting Steel Core Of Rotation

In this paper,a clad casting process of inserting steel core is proposed to obtain a homogeneous,dense and fine-grained ingots.The steel core replaces the center structure of the common ingot after being inserted into the molten steel.It completely eliminated the center porosity and shrinkage of ingot.The steel core of low temperature absorbs the heat of the molten steel and improves the undercooling,solidification speed and nucleation rate of the molten steel.The dendrites are broken in the weak place by implanting steel core of rotation,which improves the refinement and uniformity of solidification structure.The clad casting experiments were carried on with 20 steel as the steel core and with Q235 steel as the melt.The influence of process parameters on the internal quality of ingot was analyzed by comparing the macromorphologies and microstructures of ingot under different conditions.In the experiment,the steel core is a diameter of 40 mm,the length of 320 mm.The rotating speed is 120 rpm and the preheating temperature is 120 ℃.The macromorphologies of ingot shows that there is no porosity and shrinkage at the center of ingot.There are a large number of shrinkage cavities in the top position and a small number of holes near the liquid-solid interface.The observation shows that the solidification structure of the ingot is greatly fine.The average grain size of the ingot is only 42 μm in comparison with the ingot without steel core.After the steel core is inserted into the molten steel,the undercooling of the melt is larger and the nucleation rate is higher near the steel core.At the same time,the solidification rate of melt is also larger near the ingot mold.The melt solidifies simultaneously at inside and outside.It refined the solidification structures of ingot due to the decrease of solidification distance.The results of microstructure comparison show that when the solid-liquid ratio is 1 :12.7,the amount of melt is more,the heat transfer distance of solidification is larger,and the porosity is easy to appear at the last solidification position.When the solid-liquid ratio is 1 : 9.5,the amount of melt is not much,and a small amount of holes appear at the liquid-solid interface due to insufficient feeding.The results show that the grains are broken by the rotating steel core in the weak position,the nucleation rate of the melt increases,the number of grains increases,meanwhile the rotating steel core makes the solidification structure more uniform.When the preheating temperature of the steel core is different,the results of microstructure comparison show that when the preheating temperature of the steel core is low,the undercooling of the molten steel near the steel core is large,and the grains formed aresmall.When the preheating temperature of the steel core is high,the surface of the core is melted,and the liquid-solid interface is better.When the steel core directly falls into the melt after rotation,the insufficient feeding inside the ingot is improved,the holes at the liquid-solid interface are eliminated,and the porosity inside the ingot is almost eliminated.The experimental results of normalizing and thermal simulation compression show that the microstructure of ingot is more compact and uniform,and the average grain size in solidification microstructure is reduced to about 14 μm.When the ingot samples are compressed along the direction perpendicular to the liquid-solid interface,the liquid-solid cladding is more compact,the interface defects are obviously reduced,and the interface cladding degree is improved.The results of microstructure comparison between common ingot and composite ingot after one normalizing show that the solidification structure of the composite ingot is more uniform and compact than that of the common ingot,and the grain size is smaller when the rotating speed of the inserted core is larger.